A manual of botany, anatomical and physiological : for the use of students / by Robert Brown.
- Date:
- 1874
Licence: Public Domain Mark
Credit: A manual of botany, anatomical and physiological : for the use of students / by Robert Brown. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![buried in the soil, out of reach of the necessary conditions of existence—though it must be remembered, also, that the wind may have wafted some of them from a distance [See Phyto- Geography]. Seeds enveloped in wax have preserved their vitality for long periods, probably owing to oxygen having no access to the embryo. It ought, however, to be mentioned, that the absolute necessity of seeds having access to air, in order to allow of the action of oxygen upon them, is not universally conceded by physiologists, since Edwards and Collin consider that the oxygen which com- bines with the carbon of the seed, and forms the COo which is expelled in germination, is obtained, not necessarily from the air, but by the decomposition of water.^ Becquerel and Boussingault'' also consider that lactic acid is constantly formed during germina- tion, and Edwariis and Collin that acetic acid is formed during the same process, and that it is owing to the formation of this, and not to the formation of COg, that the carbon of seeds is lost— an opinion which we consider hardly tenable in the face of known facts. 4. Light and Darkness.—Contrary to the opinion of most botan- ists, and nearly all gardeners, it does not appear that light exercises any appreciable deleterious influence on germination,—Theodore de Saussure and Meyen having found that the seeds they experi- mented on vegetated in perfect darkness and daylight equally well; and these experiments the writer has repeated with much the same results.^ The deleterious influence usually attributed to light may be owing to the unfavourable effect which light and heat exercise by drying the soil. In another experiment, Saussure caused seeds to be planted under two cloches, or bell-jars, of equal capacity and under exactly similar circumstances ; but one of these cloches was rendered opaque, while the other was left transparent. Under the transparent one the seeds germinated much more quickly than under the darkened one, showing that light exercises no deleterious influence, but probably a beneficial effect, by affording, as in this case, great heat without any sub- traction of moisture to the seeds. Some plants, indeed—e.g., heath and calceolarias — germinate better when uncovered by earth; and though seeds are buried in the soil away from light, yet many will germinate perfectly well if scattered on the surface, as they are naturally by the dehiscence of the fruits. Hunt, and more recently M. P. Bert, in a report presented 1 Comptes rendus, vii. 922 ; and Boussingaulfs Econ. rurale, i. 37. 2 Ibid., vi. 102. ^ See also Hoffmann's experiments (in Jahresbericht iiber Agrikultur Chemie, 1864, s. 110) with twenty-four kinds of agricultural seeds—the result of which was, that light exercised no appreciable influence on germination.](https://iiif.wellcomecollection.org/image/b21931902_0556.jp2/full/800%2C/0/default.jpg)
